Having used both Torque Pro and MiniVCI, MiniVCI is best hands down as a diagnostic tool. Period. At <$30, it's barely more than bluetooth OBD and Torque Pro at about $18. This assumes one has a suitable laptop for installation. Torque Pro is a great tool, and it's more practical for continuous monitoring given the portability.
Several years ago, a Gen 1 with 320,000 miles was lost in a traffic accident. It was running on the original battery. Heat is the enemy and that is what metrics can provide. Bob Wilson
after over 20 years of driving my 2002, I saw this charging situation last night. Driving on freeway it charged up to about 96% and stayed there for maybe 10 minutes. then in discharged back down to about 55% and stayed there until I reached my destination about 10 minutes later. Upon driving home about 2 hours later, it maintained about 65% charge. About 170000 miles, original battery
You should have been watching voltage difference between the Hybrid Battery Cells. I had a similar experience when my initial Project Lithium Battery failed after 3-days. Whenever voltage difference spiked significantly upon regen braking... State of of charge would shoot up to 80+٪ in a matter of seconds. You can watch this happen in my YouTube vid here: Watch starting around 3-minutes you'll see my State of Charge parameter spike to over 85% whenever voltage difference spikes under regen brake. If you'd like the full context to this video... see my thread: I think my Project Lithium Battery failed in 3-days.
The poster does not say anything about having a Lithium Ion battery. Also of note, the poster's car is a Gen 1 (this is the Gen 1 forum after all!) and I believe what the poster observed is a normal mode in a Gen 1. ChapmanF has commented in the past noting this behavior and hopefully, he will see this thread so and jump in and fill in the blanks.
Cell balance is a valid concern. He may have gone through the mythical rebalance cycle. Compared to what we have today, the earlier battery management systems were primitive. Bob Wilson
Well, about the best I can do is google for the threads where I posted about it before. Those were, well, post #4 in this very thread and, a couple years later, this other thread where I gave more details when it happened again.